The manufacture of a tool, or pattern, has conventionally involved machining from a billet of material, an additive process such as casting from a mould, sculpting or fettling, or fabrication, for example from sheet metal. For large scale tools, typically required in the aerospace and automotive industries, the length of time in preparing tools by such methods is slow, and is prohibitively expensive. This is due in part to the large size of the billets of material required, which must be committed to the tools in their manufacture, and which may have to be ordered months in advance of their supply.
Furthermore, the amount of skilled labor time and material required in producing a tool conventionally has made it uneconomical to produce a tool for limited volume production, for example in product development, limited batch production and mass customization.
In order to overcome these problems, reconfigurable modular tools have been developed, typified by that disclosed in U.S. Pat. No. 5,846,464. In the tool disclosed in this patent, an array of vertically adjustable pins are mounted on a drive base, such that the height of each pin above the base can be individually set. A flexible surface, or face sheet, is attached to flexible supports, which are mounted at the ends of the pins. The surface contour of the face sheet can therefore be set to a desired contour by adjusting the individual heights of the pins. The adjustments are controlled automatically through a computer, which is pre-programmed with the desired contour. When the tool is in use, the face sheet surface acts either as a primary tooling surface, or as a secondary tooling surface for producing a pattern or mould, for example, for casting.
Reconfigurable tools of the kind described are suitable for some applications, but for other applications do not have sufficient robustness and/or definition in the tooling surface. The pins which support the flexible face sheet are spaced apart, and do not lie in the plane of the desired surface contour. Therefore the face sheet surface is only a point to point approximation of the desired surface contour. The resolution of the surface is dependent on the density, number and size of pins in the tool array, but as the density of the pins increases, and their size reduces, it becomes increasingly difficult to adjust the positions of the pins.
The combined strength of the pins is also much less than the strength of a solid tool, and therefore the tool is not strong enough for the majority of tooling operations. Furthermore, the aspect ratio, that is, the range of depth in the tooling surface in comparison to its width, is limited by the amount the face sheet can deform.
It has also been proposed in GB patent No. 868,162 to provide a device for supporting workpieces during machining, including a holder in the form of a housing frame or body having an array of vertically adjustable plungers mounted therein, together with thrust-transmitting, vertically-disposed packing pieces between these plungers, and a device for exerting pressure laterally to the plungers through the packing pieces to clamp them in adjusted position.